[PD] emulating an acoustic hi-hat pedal

[Andy Farnell]

Hey Patrick,


It's the "everything in-between" bit that is hard. A hihat is one
of those instruments that seems really simple, but on deeper analysis
you see it is an amazingly complex and subtle device (which is obvious
when you hear a really good drummer playing). With samples you can get
the usual opening and closing strike sounds, and the cup/clash.

But if you want a really good model you probably need to look at 
physical modelling and granular methods. 

The two parts can rattle against each other causing new excitations.

Sometimes the top cymbal rotates around the bottom one, creating a 
rolling 'clatter'.

The pressure of the pedal pushes them together harder increasing
the frequencies (speeding up the roll - like if you push down
in the middle of a rolling dinner plate) and damping both parts more.

You can hit it on the edge or at any radius from the centre. As a simple
rule the spectral complexity increases as you move outwards, hitting
the bell in the middle produces a purer, shorter tone.

You can use the tip of the stick, or brush, or hit lower down
to get a less elastic impact with more energy transferrence (louder
and noiser).

So for the input vector; for pedal you probably want two continuous
ranges, position and pressure (where they are touching), and for 
excitation you probably want two more impact event parameters, 
energy (0.5 * mass * velocity^2) and duration (impulse).

You can also model leaving the stick connected, which damps the 
vibration at one point and reduces the modes.

A full physical model of two interacting centre supported circular 
plates is certainly too expensive. FM methods can give you the 
raw spectra to blend according to interaction rules. (In fact -
because the relationship of spectra in both FM and the disc modeal
model both derive from Bessel functions you can get very natural 
evolution if you choose the right synth model - complex FM with 
multiple modulator sources works extremely well.)

The trick is mapping the control params onto the synthesis params.
As they come together you can tap off a little bit of the lowest
and strongest vibrational mode (lop~ -> max~) and use it to
make impulse spikes that amplitude modulate the other plate.
Of course this is a reciprocal relationship (the lower plate
also rattles against the upper one) - so it's ring modulation
of the two maximum excusions to get a 'rattle modulator'.
Moving the lop~ up and bringing the clip down will create the
impression of the plates being forced together.

The other approach is to make a parametric map from samples
into a great big wavetable to use as grains. I have never
tried it but I think that would work well for hi-hat.

a.














On Wed, 26 Nov 2008 01:27:23 -0500
patrick <puredata at 11h11.com> wrote:

> hi,
> 
> would it be possible to patch an acoustic hi-hat pedal complete with 
> heel-splash sound, closed sound, open sound, and everything in-between.
> 
> i am not so sure where to start, i want a sampler-base solution.
> 
> adsr, playing with filters, morphing of sounds, using 2 samples or more 
> (open, middle, close, very close). i would gladly pay a beer for this.
> 
> pat
> 
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